Batch drier for grain



June 24, 1969 s. F. BURGI-IARD ETAL BATCH DRIER FOR GRAIN Sheet Filed June 8, 1967 INVENTORS 512mm: F. Suzanna BY Jog. H.W. WILMR m @440, M kmi ATTORNEYS June 1969 s. F. BURGHARD ETAL I 3,451,662

BATCH DRIER FOR GRAIN Sheet Filed June 8, 1967 fi u INVENTORS srzmm F. Buaemzn Jenn H. W. WILbIR BY LLhBo-Q, (k4, wwj w E ATTOBNEYS June 24, 1969 s. F. BURG HARD ETAL 3,451,662

BATCH DRIER FOR GRAIN Filed June 8, 196'? Sheet 3 of 3 1 3 I 33 U j T 35 3, 5 b T O O P/ 0 PULSER I RI 0] R A T] Fla 1 its? 42 o o /43 47/ 0 RELAY R SUPPLY 'R 0 PULSER 2 I 7 I I 20 4 .lNVENTORS STEPHEN F. Buaewuzo JOHN H. W.wu.os;z

United States Patent 3,451,662 BATCH DRIER FOR GRAIN Stephen Frederic Burghard, Wakes Colne, and John Herbert Wyndham Wilder, Wallingford, England, as-

signors to John Wilder Limited, Wallingford, England,

a company of Great Britain Filed June 8, 1967, Ser. No. 644,655 Claims priority, application Great Britain, June 10, 1966, 25,982/ 66; Dec. 5, 1966, 54,430/66 Int. Cl. F27b 3/00; F26b 21/10; F27d 19/00 US. Cl. 263- 13 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a grain drier preferably for drying grain in batches rather than continuously. The difiiculty with such a drier is to know when the grain is dry so that the passage of heated air through the grain can be stopped.

The invention is based on the discovery that if the inlet hot air temperature is known, the outlet air temperature is a measure of the dryness of the grain and accordingly the invention provides automatic termination of the drying time dependent on the outlet air temperature. The predetermined outlet air temperature may be arranged to be increased with time of drying in order to compensate for different "amounts of moisture in the grain.

This invention relates to a drier for grain and similar commodities, which is preferably a batch drier, that is to say, a drier which operates on batches of the commodity in turn rather than one which acts continuously to dry a commodity moving in a continuous path.

According to the present invention the drier has means for passing heated air at a predetermined temperature through the grain for drying it and includes a device arranged to measure the temperature of this air after leaving the grain and means responsive to the temperature of the air leaving the grain for terminating the drying op eration.

It has been discovered that, provided the temperature of the drying air being supplied to the grain is maintained reasonably constant at a predetermined temperature, then the temperature of the air leaving the grain is a measure of the dryness achieved and does in fact affect an averaging of the dryness of the whole content of the batch so that one does not have to measure the dryness at different samples throughout the batch.

Thus a clock does not have to be used, and pre-set, but the next stage in the cycle can commence automatically when it is indicated that the desired dryness has been achieved.

It is important to be able to dry, to a specific percentage dryness, because the density of the dried grain will vary with the degree of dryness and there will be corresponding adjustment in the price. If the grain is too wet it will not store but will rot or germinate and, similarly, if it is too dry a financial loss may occur because grain is sold on a weight basis. It appears that if a nominal 15% dryness is desired, it is acceptable if the actual dryness is Within, say, half a percent of this nominal value, but it has been discovered that for a certain crop, determining the dryness by measuring thetemperature of the air leaving the dried grain gives between 2 F. and 4 /2 F. change in air temperature for one percent difference in the dryice ness for inlet temperatures between F. and 170 B, so that it is not difficult to dry the grain to within the acceptable limits.

After the drying operation has been terminated, a cooling operation may be automatically initiated and this too can continue until a thermal responsive device indicates that the grain is sufficiently cool, so that the batch of grain can be removed from the drier and automatic re-cycling can commence by refilling with a fresh load of wet grain.

It is desirable to be able to control the inlet temperature of the heated air reasonably closely and in a preferred embodiment of the invention a pressure jet burner is used having two jets for burning oil one of which operates continuously and the second of which is switched on and off dependent upon a thermometer measuring the temperature of the air passing to the batch of grain, switching on the second jet if the temperature begins to fall and switching it 01f when it rises above the predetermined temperature.

There may also be a further temperature responsive device for shutting down the burner if the temperature of the air passing to the drier exceeds some predetermined temperature, for example, F. above which the grain would be damaged.

In some circumstances, a certain dryness of the dried grain corresponds with a temperature of the air leaving the drying zone which is greater for grains which contain more moisture before drying. Assuming that grain is required to be dried to 16% moisture content, if it contains 20% moisture before drying, the temperature of the air leaving the drying area when the grain contains 16% moisture might be 92 F., whereas the temperature for the same dryness might be 93 R, if the grain contained 24% moisture before drying. In general, the wetter the grain before drying the higher will be the temperature of the drying air leaving the drying area when the desired degree of dryness has been achieved.

Thus the drier may include a device for setting a reference temperature, and means for resetting the reference temperature automatically in response to increasing duration of the drying operation in a drying cycle.

It is clear that the wetter the grain to be dried, the longer it will take to dry the grain, and the rate of increase of reference temperature with time can be arranged to give a reference temperature corresponding with the appropriate outlet temperature representing the dryness whatever the wetness of the grain before drying.

The operator does not have to make any adjustment but merely fills the hopper with the grain to be dried and, as the drying operation proceeds, the device automatically resets the reference temperature upwards, either in steps or continuously. The temperature of the air leaving the drying area, as detected by the temperature-responsive device, will increase as the grain become drier, and in general it will increase at a faster rate than the rate of increase of the reference temperature until the time it has overtaken the reference temperature, at which time a signal is given to terminate the drying operation. The reference temperature may be arranged to remain constant after a certain time, or even be progressively reduced after a time.

There may be means for setting the initial reference temperature dependent upon the desired dryness to be achieved. Thus, in diiferent circumstances, a farmer may want to dry his grain to have 16% of water or perhaps 15% of water depending upon whether the grain is to be sold immediately or is to be stored before sale and this he can do by selecting the initial reference temperature. The higher he sets the initial reference temperature, the longer will it take for the outlet air temperature to overtake the increasing reference temperature and so the longer will be the drying period and the greater the degree of dryness achieved.

There may also be means for setting the rate of increase of the reference temperature with time, for example by setting a clock or a pulse generator for operating the device so that the reference temperature is reset at a greater or lesser rate. Seed, for example, in general requires to be dried more slowly than grain if the seed is still to remain capable of germination and this can be achieved by use of this control. The same dryness can be achieved in the same Way, but it can be arranged to take longer.

In a preferred embodiment of the invention the temperature responsive device is arranged to give successive electrical signals as the temperature measured increases through discrete steps and the device is arranged to generate successive electrical signals corresponding to increasing reference temperatures and a simple circuit can make a comparison and give a signal when the measured temperature has overtaken the reference temperature.

The temperature of the air leaving the drier may be measured by a thermometer of the kind having a number of electrical contact wires sealed into the mercury tube, so that as the mercury rises up the tube it will make electrical contact with the different contact wires in turn. The contact wires may be connected to diiferent fixed contacts on a uni-selector switch having a moving contact or an electronic switch with no moving parts which is arranged to connect contacts in turn in a relay circuit, each step being in response to a pulse generated by a variable fre quency pulser. The relay is operated to switch off the burner when the mercury reaches a contact wire which is connected in the relay circuit as the measured temperature overtakes the reference temperature.

In another possible arrangement the temperature is measured by a variable resistance type of thermometer which gives a voltage at a wiper contact which increases with increasing drying air temperature.

Balance can be detected by means of an electrical bridge having resistances responsive respectively to (a) the temperature being measured, (b) the changing reference temperature, (c) a fixed value, and (d) an adjustable value for calibration purposes.

One pulsing device which may be used has a small mercury switch which is driven to and fro by a geareddown motor, the mercury making with a contact at one endof its glass bulb each time the switch reaches the end of its travel. A system of this kind can be arranged to generate pulses at frequencies from a few seconds to a substantial part of an hour.

The invention may be carried into practice in various ways and one embodiment will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a sketch showing the general arrangement of a batch drier housing embodying the invention;

FIGURE 2 is a circuit diagram of the control system;

FIGURE 3 shows a modification of the circuit diagram, and

FIGURE 4 shows an alternative control arrangement. The compartment for each batch of grain to be dried is of generally annular constant cross-section along a horizontal axis and may be defined as the space between expanded metal inner and outer hexagonal shaped casings 11 and 12, and closed ends. Grain is fed into the compartment from a hopper 13 at one end by means of a screw feed 14 driven by an electric motor for taking the grain from the hopper towards the other end of the casing. A fan 15 at one end of the interior of the inner casing 11 draws drying or cooling air through the grain in generally 4 radial directions from an enclosure surrounding the outer hexagonal casing 12. This enclosure 16 defines a distribution space for the air which enters at the lower part of one end of the enclosure through a chamber 17 by way of a burner 18 which might burn gas or oil, or might be electric.

The batch drier is thus enclosed and operates by radially inwardly flowing hot air through the grain. At the lower part of the grain compartment between the casings 11 and 12 a second screw feed 19 is used for removing a batch of dried grain in preparation for receipt of the next wet batch at the top and this feed 19 is also driven by an electric motor.

The relays for switching the motors on and off are shown at A and C in the control circuit of FIGURE 2, the relay A being for the motor for the feed 14 for supplying moist grain and the relay C being for the motor driving the feed 19 for removing the dried grain.

FIGURE 1 also shows a top pressure switch H mounted at the far end of the feed 14 which operates to close an electric contact in the circuit of FIGURE 2 when the grain rises sufiiciently indicating that the drying chamber is full. Similarly there is a bottom pressure switch I which also has a contact in the control circuit which is closed about half way through the filling operation and which opens again when all the grain has been removed and the drier is ready for the next batch of wet grain.

The automatic recycling operation of the batch drier will be understood best from the description of operation of the control circuit in FIGURE 2.

T1 and T2 are clocks which can be pre-set to any desired time interval and which each have two contacts which close in turn with an interval of about five minutes, the first one closing after the clock has run for the preset time. The clocks run as long as an electrical supply is maintained through their motors both contacts of a clock return to the normal positions when the electrical supply is removed from an energising winding F associated with that clock. The clocks are then ready for a new cycle when the windings F are again energised. It is to be noted that the clocks remember the pre-set time from cycle to cycle and do not have to be set each time as with an egg-timer type of clock.

The burner 18 in FIGURE 1 has a control shown at E in FIGURE 2 and this control includes a circut for energising a lock-out relay D whenever a photo-electric device detects that the burner has gone out and the air is no longer being heated. For the purposes of this description it is sufiicient to say that the burner operates whenever there is an external connection between the terminals marked 8 and 6 on the control.

As has been described above the relays A and C are for operating the loading and unloading motors driving the feeds 14 and 19, while the relay B is used to switch on the fan 15 for inducing the flow of hot and cold air through the grain. T4 is a hand operated clock which can be set to prevent refilling of the drier after a set time, perhaps because the supply of grain will be exhausted by that time or because only a certain number of loads are to be dried.

The operation of drying a batch may be summarised as follows: After filling the drying compartment the grain is dried for about 2 hours using air at a temperature of about F. This is followed by drawing cooling air through the grain but with the burner not operating, for 15 to 20 minutes after which the unloading feed starts to empty the drier at the end of that cycle. It should be explained that these temperatures and times are examples suitable for particular grain in a particular state and experience will determine the setting in a particular case.

The operation of the automatic control system will now be described and it is believed that the nature of the control circuit shown in FIGURE 2 will become apparent from this description without its being first described in detail.

It will be noticed that at starting, the switches H and J '5 will be in the open position shown in FIGURE 2 so that there will be no supply to the relay B for energising the fan motor and no supply to the energising windings F of the clocks T and T and also no supply to the relay C for the unloading motor.

Initiation of automatic operation is by hand operation of three switches W, X, and Y so that the contacts W X Y in series are all closed to connect the control circuit supply from the mains line L to the contacts of the switches H and J and to the relay A of the loading motor through the normally-closed contacts T T B and C In consequence the main switch S for the loading motor is closed to start the loading motor so that the grain is fed from the hopper 13 through the loading feed 14 into the drying compartment.

Closing of the switch W ensures that a switch W for hand operation of the loading motor remains open, and similarly, closing of the switch contacts X and Y ensures that contacts X and Y remain open to prevent hand operation of the fan motor and the unloading motor. A contact X closes at the same time to enable the fan motor relay B to be energised when the supply becomes available.

Once the relay A has operated, its contact A closes to short circuit the normally closed contact T 1 of the clock T Thus the clock can only prevent starting of a filling operation and cannot stop it once it has started. Its contact can also be shorted by a hand-operated contact V. Also the contact A opens to ensure that the relay C for the unloading motor cannot become energised when the switch I closes.

Loading continues until when the drier is about half full of grain the switch I closes to provide the energising supply to the winding F of the clock T However, the relay C is not energised because the contact A is open.

Eventually when the drier is full, the switch H closes to energise through the contacts T No. 2 and X the relay B for the fan motor, and in consequence the fan motor switch S closes. The contact B opens to de-energise the relay A so that the loading motor stops and the contact B closes to maintain the supply across the relay B in spite of any opening of the switch F for example due to the grain level falling as the grain is dried. The contact B opens to maintain the relay C tie-energised in spite of closing of the relay contact A and the contact B closes to provide the supply for the burner 11 which ignites provided a manual switch Z has been closed, so that the hot air is delivered to the fan through the grain in the drying chamber. This state of affairs continues until a temperature responsive device detects that drying has been completed.

The temperature responsive device is situated within a discharge duct 20 (FIGURE 1) leading from the fan 15 to be responsive to the temperature of the air leaving the drying compartment. It may be considered to operate to close a contact S in series With the relay R in the circuit of FIGURE 2 when a preset temperature is achieved. The relay R has four contacts. The first contact R is a normally closed contact in series with the normally-closed contact C for preventing operation of the filling relay A when the relay R is operated. A self-holding contact R closes when the relay R is energised to hold it in, a normally-open contact R closes to start the cooling timing clock T when the relay R is energised, and a normallyclosed contact R de-energises the burner E once the detection of the correct temperature has indicated that the grain is dry.

A manual switch has a contact U which when open isolates the common contact of the switch T 2 from the supply and also isolates the clutch coil F of the clock T and an alternative contact U which when closed completes an energisation path for the relay R provided the switch S is closed. Thus if the operator closes the switch U operation is as described above, but if instead he closes the switch U the drying time is determined by a preset clock T The fan continues to run until at the end of the cooling time the contact T N0. 1 opens (to prevent subsequent energisation of the relay A when the relay B is released) and five minutes after this the contact T N0. 2 opens to remove the supply from the relay B and stop the fan.

Release of the relay B causes the contact B to close although the relay A is not re-energised because the contact T N0. 1 is now open. The contact B opens and also the contact B to prevent re-ignition of the burner 11 in consequence of the closing of the contact T N0. 1.

Also the contact B closes so that now the relay C is energised through the switch I and the contacts A and B This starts the unloading motor through its main switch S and the dried and cooled grain is unloaded from the drier until when it is empty the switch I switches back to the position shown in FIGURE 2 and the relay C is released. During operation of the unloading motor the contact C is open to prevent re-energisation of the relay A and when the switch I opens the energising supply is removed from the winding F of the clock, T so that its contacts T N0. 1 and T N0. 2 are in the position shown in FIGURE 2. in preparation for the next cycle which begins again automatically as soon as the contacts T N0. 1, B and C are all once again closed.

Each of the main switches S S and S has an overload coil in each phase capable of operating an overload trip which in the conventional use of a direct-on-line starter would operate to open a contact in the circuit of the operating relay A, B or C. However, in the present circuit the overload trip contacts SA 5B SC are connected in series in the supply to the control circuit so that if any one of the motors is overloaded the control circuit is de-energised and everything shuts down.

In practice one can estimate from experience the control time to be allowed for cooling.

In a modification of the invention, instead of having a simple switch S which operates when the temperature of the air leaving the drying chamber reaches a predetermined temperature, an additional control is provided to take advantage of the fact that in some cases the wetter the grain is before drying the higher will be the temperature of the drying air leaving the drying chamber when the desired degree of dryness has been achieved. It is clear that the wetter the grain to be dried, the longer it will take to dry the grain, and accordingly the preset temperature at which drying is automatically terminated is arranged to be increased progressively.

For this purpose the circuit of FIGURE 2 is modified as shown in FIGURE 3. The modifications only concern the connection to the relay R and in other respects the circuit is similar.

Instead of having the switch S directly operated by a temperature responsive device, a relay Q has a normally-closed contact Q1 for energising the relay R, when the relay Q is released, to terminate the drying operation and commence the cooling operation timed by the clock A control circuit for the relay Q includes a temperature responsive potentiometer 31 which is arranged automatically to increase in resistance over a set range for a selected increase of temperature in the range 5 F. to 22 F. This temperature responsive device 31 is connected in a bridge arrangement with two equal resistors 32 and 33 and a control potentiometer 34 having a wiper which can be driven in steps by a motor 35 to be progressively increased or decreased in dependence on the setting of the contact P1 of a timer P. At switching on, the resistance of the temperature responsive device 31 will be lower than the resistance of the potentiometer 34 so that the bridge will be unbalanced and a relay N connected across one diagonal will be energised, and its normally-open contact N in series with the relay Q and the supply will be closed to energise the relay Q and hold the contact Q1 open.

During automatic operation with the switch U open and U closed, as soon as drying commences with energisation of the relay B in FIGURE 2, the contact B closes to energise a pulser 36 and a timer P. The timer P runs for a predetermined time for a purpose which will be described below. The pulser 36 can be set by means of dials 37 and 38 to emit operating pulses for the motor 35 with a duration which can be set by the knob 37 and an interval between pulses which can 'be set by the knob 38. Both pulse duration and pulse interval can be varied between 1 and 57 seconds.

As drying continues, the resistance of the potentiometer 31 increases as the temperature of the air leaving the drying chamber increases due to the progressive drying of the grain. However, the pulses supplied to the motor 35 will gradually increase the resistance of the potentiometer 34 so that it takes longer for the resistance of the temperature responsive potentiometer 31 to equal that of the potentiometer 34. When the two resistances become equal, the bridge will be balanced and the relay N will release so that its contact N opens to de-energize the relay Q and allow its contact Q to close to energize the relay R. This will terminate the drying step and start the cooling step in the manner described above. It should be noted that additional contacts on the relay R are used; the contact R disconnects the output of the pulser 36 from the motor 35 and the contact R closes to provide continuous energisation of the motor 35 to reset it to its lowest value ready for the next batch of gram.

It will be seen that the wetter the grain to be dried the higher will be the resistance of the controlled potentiometer 34 so that a longer time will be taken for the potentiometer 31 to reach this resistance value and balance the bridge and terminate the operation.

The temperature of the air leaving the drying chamber at which termination occurs increases progressively from perhaps 80 F. to 100 F. over a time (for example 1 hour) which can be selected by adjustment of the pulser 36 and adjustment of the differential of the temperature responsive potentiometer 31. After a time, further increase of the termination temperature is not required, and for some grains it may be required to drop progressively after a time.

If the resistance of the potentiometer 31 has not reached the resistance of the potentiometer 34, in a time set on the timer P, the resistance of the potentiometer 34 can be kept constant or can be arranged to be driven in the re verse direction. This is effected merely by opening or changing over the contact P which causes the pulses from the pulser 36 to cease to be effective, or to act in the reverse direction, in accordance with the characteristic desired. Eventually, when the bridge becomes balanced, the drying operation will be terminated.

If, as with the embodiment of FIGURE 2, it is considered sutficient if a straight detection of the temperature o Fthe air leaving the drying chamber is used to terminate the drying operation, the potentiometer 34 can be set and maintained at a resistance equal to the resistance of the temperature-responsive potentiometer 31 for the required temperature at which termination is to occur and indeed in equipment where this was always considered to be sufiicient the pulser 36 and timer P would not be required.

It should be noted that with this invention it is always preferred that the drying air entering the drying chamber is at a constant known temperature.

The heater 18 has two fuel burning jets, one of which 18' operates continuously while the other of which 18 is switched on and ott in dependence upon a thermometer 22 measuring the temperature of the air passing to the grain.

In an alternative arrangement shown in FIGURE 4 the temperature of the air leaving the drier at 20 is measured by a thermometer 41 having a number of electrical contact wires 42 sealed into the glass tube for the mercury so that as the mercury rises it will make contact with the wires in turn.

The wires 42 are connected to an electronic switching circuit 43 operated in steps by the pulser 36 so that the different wires 42 are connected in turn in series in a circuit including the relay Q whose single contact is a normally-open contact in series with the relay R in the circuit of FIGURES 2 and 3. When the mercury 44 reaches a contact wire 42 connected in the relay circuit, the relay Q operates to terminate the drying operation by energising the relay R.

As with the circuit of FIGURE 3, if desired, the timer P can be used to prevent operation of the switch 43 after a time or even to cause it to reverse and step the reference temperature downwards.

There might be 20 contact wires 42 in steps corresponding to 1 F. difference of temperature.

What we claim as our invention and desire to secure by Letters Patent is:

1. A grain drier including means for passing heated air at a predetermined temperature through the grain for drying it, and a device arranged to measure the temperature of the air after leaving the grain and means responsive to the temperature of the air leaving the grain rising to a certain temperature for terminating the drying operations and initiating a further operation on the grain.

2. A drier as claimed in claim 1 including a device for setting a reference temperature and means for resetting the reference temperature automatically in response to increased duration of the drying operation of a drying cycle, in which the responsive means terminates the drying operation when the temperature of the air leaving the grain reaches the reference temperature.

3. A drier as claimed in claim 2 in which the reference temperature is arranged to be progressively increased as drying continues.

4. A device as claimed in claim 3 in which the reference temperature is arranged to stop increasing after a predetermined time, and to remain constant or to decrease progressively.

5. A batch grain drier as claimed in claim 1 including means for automatically loading the drier, drying the grain and unloading the drier in a drying cycle in response to the temperature responsive means, and for automatically recycling.

6. A drier as claimed in claim 1 including means for maintaining the heated air for drying the grain at a constant temperature related to the said certain temperature.

7. A drier as claimed in claim 6 including a burner for heating the air, which burner has two jets for burning fuel one of which operates continuously and the second of which is switched on and oit in dependence on a thermometer measuring the temperature of the air passing to the grain.

8. A drier as claimed in claim 1 in which the temperature measuring device comprises a variable resistance thermometer.

9. A drier as claimed in claim 1 in which the further operation of said responsive means is a cooling of the grain.

10. A drier as claimed in claim 1 in which the further operation of said responsive means is an unloading of the grain.

11. A drier as claimed in claim 1 including a variable resistance thermometer for measuring the temperature of the air leaving the grain in which the variable resistance element of the thermometer is connected in an elec- 9 trical bridge arrangement which is arranged to be balanced when the resistance of the thermometer is equal to the resistance of another component of thebridge which is arranged to be progressively reset.

12. A drier as claimed in claim 2 including means for adjusting the rate of resetting of the reference temperature.

13. A drier as claimed in claim 12 including a pulse generator whose pulses cause successive resetting of the reference temperature and clock means for controlling the interval between pulses or the duration of pulses or both.

References Cited UNITED STATES PATENTS 7/1961 Pierpoint 3455 9/1962 Applegate 263-30 6/1963 Figley 34167 8/1965 Williams et a1. 263--l0 10/1962 Andersen 3445 10/ 1968 Burghard 3456 US. Cl. X.R. 

